The following patents and/or commonly assigned patent applications are hereby incorporated herein by reference:
This invention relates to the field of electronic assemblies, more particularly to thermal management in spatial light modulator display systems.
Proper thermal dissipation is necessary to ensure reliable operation of many electronic devices. Many devices use heat sinks to allow thermal energy to be exhausted to either a cold wall or a cooling stream of air. Spatial light modulators, such as the digital micromirror device or DMD, provide unique thermal challenges. Not only does the electrical operation of the DMD create heat, the micromirrors absorb a portion of the intense beam of light focused on them, dramatically increasing the temperature of the micromirror device. Furthermore, the necessity of a free optical path to the surface of the micromirror array prevents the use of conventional heat sink methods.
A conventional DMD package and heat sink is shown in FIG. 1. In FIG. 1, the micromirror array typically is packaged in a ceramic or plastic substrate 102 sealed with a glass lid 104. Electrical connections between contacts on the rear surface of the micromirror package and a printed circuit board 106 are provided by an interposer 108. Several types of interposers 108 may be used. The interposer 108 may be an insulative resilient material having conductive portions in contact with the contacts on the micromirror package and electrical contacts on the printed circuit board. Alternatively, a plastic interposer 108 with metal spring contacts may be used. The DMD and interposer 108 are held in contact by a socket, not shown in FIG. 1, mounted over the DMD.
To remove heat from the DMD, an opening through the printed circuit board is used to allow a thermal stud 110 to contact the micromirror package substrate 102 from the back. A heat sink 112 is attached to the end of the thermal stud. The thermal stud 110 is epoxied to the back of the micromirror device using an epoxy patch 114. Another epoxy patch 116, or mechanical fasteners such as machine screws, are use to attach the heat sink 112 to the thermal stud 110. While this arrangement is quite effective to remove the heat from the micromirror package, it is difficult and expensive to produce.
The method used to attach the thermal stud to the package begins by inspecting the thermal stud 110 for defects, indentations, and sharp corners. The electrostatic integrity of the stud attachment fixture is then verified. The fixture pocket is cleaned, and then the micromirror package is loaded into the fixture pocket with the bottom surface up. The bonding surfaces of both the package and the stud are then wiped clean. An alignment plate is placed over the device in the stud attachment fixture. The thermal stud is placed on a hot plate to warm it. An epoxy patch is attached to the bonding surface of the thermal stud and the thermal stud is placed through the opening of the alignment plate and onto the micromirror device. A weight is then placed on the thermal stud and the epoxy patch is allowed to cure. When the epoxy patch has cured, the attachment is subjected to a shear force to verify the integrity of the attachment.
The process is not only labor intensive, it is also difficult to control. Due to inconsistencies from batch to batch of the epoxy patches and other process variations, the thermal stud attachment process often fails to achieve sufficient bond strength. If the bond fails the device must be scrapped because the thermal stud cannot be epoxied onto the micromirror a second time. An improved apparatus and method of extracting heat from the micromirror package is needed.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention which provides a method and system for attaching a thermal stud to an electronic package. One embodiment of the present invention provides a method and apparatus for attaching a heat sink.
Another embodiment of the present invention provides a method of attaching a heat sink to an electronic device. The method comprises: providing an anchor surface having a first side and a second side; positioning an electronic device on the first side; placing a heat sink against the electronic device, the heat sink extending to the second side of the anchor surface; and retaining the heat sink against the electronic device using a spring clip.
Another embodiment of the present invention provides an electronic assembly comprising: an anchor surface having a first side and a second side; an electronic device on the first side; a heat sink in thermal communication with the electronic device, the heat sink extending to the second side of the anchor surface; and a spring clip holding the heat sink against the electronic device.
Another embodiment of the present invention provides an electronic assembly comprising: an anchor surface having a first side and a second side; an electronic device on the first side; means for heat sinking the electronic device in thermal communication with the electronic device and extending to the second side of the anchor surface; and means for holding the heat sink against the electronic device.
Another embodiment of the present invention provides a display system comprising: a light source for providing a beam of light along a light path; a display controller for providing image data; an anchor surface having a first side and a second side; spatial light modulator on the first side, the spatial light modulator on the light path and operable to modulate the beam of light in response to the image data; a heat sink in thermal communication with the spatial light modulator, the heat sink extending to the second side of the anchor surface; and a spring clip holding the heat sink against the spatial light modulator.